Novel Metal Detector Finds Lost Screws -- MEDICA - World Forum for Medicine

Orthopaedic surgeons often need to remove orthopaedic screws that shift position, trigger an infection or cause pain, but skin and scar tissue can make it difficult to find the troublesome hardware, even with the aid of real-time X-ray technology. A small handheld detector by eight biomedical engineering majors at Johns Hopkins University is designed to zero in on the hardware and steer the doctor's screwdriver into position for prompt removal.

"Our device is set up so that if no metal is near the search coil, there is no sound. But as the detector comes closer and closer to a piece of metal, like a screw, it sends out a tone that rises higher and higher in pitch," said Eli Luong of Garden Grove, Calif., one of the two leaders of the student design team. The search coil is located inside the slender tube. These two parts of the probe together form a device that the doctor can insert during a minimally invasive procedure. First, a small incision is made near the expected site of a tiny orthopaedic screw that needs removal. The probe is then inserted to help the doctor home in on the head of the screw.

When the screwhead is found, the coil detector is carefully removed from the probe's hollow tube. The two-part design resembles the cannula and trocar tools commonly used in biopsies. After the coil detector segment is taken out, the doctor inserts a screwdriver through the tube section, which remains perfectly positioned for removal of the screw.

"During our research, many of the orthopaedic surgeons we talked to showed interest in our device. They said they usually have to remove five to ten percent of the screws they've implanted," said Jennifer Hoi of Belmont, Calif., the other team leader. "That's why we believe this device would be a useful addition to every orthopaedic operating room and every surgeon's toolbox."; Source: Johns Hopkins University